The invention relates to an electrochromic optical device and a method to manufacture the same. The invention may be used in optical devices such as windows, mirrors and high-contrast non-emissive display elements.
Electrochromism is known in oxides based on W, V, Ni, Mo, Ir, etc, and in numerous organic substances. Change in optical properties is caused by the injection or extraction of mobile ions. A material colouring, i.e. lowering its transparency, under injection or extraction is referred to, respectively, as cathodic or anodic material. Absorptance modulation as well as reflectance modulation are possible.
A practical coating in a device, for example having the form of a window, could comprise an electrochromic thin film integrated in an all-solid-state multilayer configuration.
It is known that one can form an optical device of this kind with two outer transparent conductors, required for applying the electric field, an electrochromic layer, an ion conductor in the following also mentioned as electrolyte, and an ion storage. This configuration is backed by a transparent substrate such as a glass pane; alternatively the configuration can be interposed between two transparent substrates. Coloration and bleaching are accomplished when ions are moved from the ion storage, via the ion conductor into the electrochromic layer or when the process is run in reverse. The ion storage can have the form of another electrochromic layer, preferably anodic if the base electrochromic layer is cathodic, or vice versa. By use of a purely ionic conductor, one can obtain an open circuit memory, i.e. the electric field has to be applied only when the optical properties are to be altered.
From French Patent No. 2 568 574 is known a solid state polymeric conductor usable in optical devices of the type described. As the polymer is suggested poly(ethylene glycol). It is also known that poly(propylene glycol) (PPG) also known as poly(propylene oxide) . . . diol, doped with metal salts (e.g. lithium, sodium or potassium) are relatively good ionic conductors. It is also known that poly(ethylene oxide) (PEO) and its diol poly(ethylene glycol) (PEG) are even better ion conductors at temperatures greater than 60.degree. C. Ratios of ether oxygen to metal in the range 9:1 to 25:1 produce the best conductivities in these series-some conductivities (for doped PPG) reaching as high as 5.times.10.sup.-5 S cm.sup.-1 at 25.degree. C.
These prior known electrolytes are hygroscopic. In addition, doped PPG is fairly fluid in the range of good ionic conductivity, and doped PEO is crystalline below about 60.degree. C. In a commercial product not only properties relating to the basic functions have to be considered, but also demands relating to the production and handling have to be fulfilled. A hygroscopic electrolyte will in practical use give a product with limited applicability or at least the necessity to build the device as a hermetically sealed casset. If, on the other hand, the electrolyte has a low solidity, i.e. it is fluid or gelatinous, or has a low adherence to pertinent surfaces it can not be integrated in the device as a carrying part of the same.